Network topology

About: Network topology is a research topic. Over the lifetime, 52259 publications have been published within this topic receiving 1006627 citations.

The Accordion Phenomenon: Analysis, Characterization, and Impact on DTN Routing

Abstract: We analyze the dynamics of a mobility dataset collected in a pipelined disruption-tolerant network (DTN), a particular class of intermittently-connected wireless networks characterized by a one-dimensional topology. First, we collected and investigated traces of contact times among a thousand participants of a rollerblading tour in Paris. The dataset shows extreme dynamics in the mobility pattern of a large number of nodes. Most strikingly, fluctuations in the motion of the rollerbladers cause a typical accordion phenomenon - the topology expands and shrinks with time, thus influencing connection times and opportunities between participants. Second, we show through an analytical model that the accordion phenomenon, through the variation of the average node degree, has a major impact on the performance of epidemic dissemination. Finally, we test epidemic dissemination and other existing forwarding schemes on our traces, and argue that routing should adapt to the varying, though predictable, nature of the network. To this end, we propose DA-SW (density-aware spray-and-wait), a measurement-oriented variant of the spray-and-wait algorithm that tunes, in a dynamic fashion, the number of a message copies disseminated in the network. We show that DA-SW leads to performance results that are close to the best case (obtained with an oracle).

The Topological and Electrical Structure of Power Grids

Abstract: Numerous recent papers have found important relationships between network structure and risks within networks. These results indicate that network structure can dramatically affect the relative effectiveness of risk identification and mitigation methods. With this in mind this paper provides a comparative analysis of the topological and electrical structure of the IEEE 300 bus and the Eastern United States power grids. Specifically we compare the topology of these grids with that of random [1], preferential-attachment [2] and small-world [3] networks of equivalent sizes and find that power grids differ substantially from these abstract models in degree distribution, clustering, diameter and assortativity, and thus conclude that these abstract models do not provide substantial utility for modeling power grids. To better represent the topological properties of power grids we introduce a new graph generating algorithm, the minimum distance graph, that produces networks with properties that more nearly match those of known power grids. While these topological comparisons are useful, they do not account for the physical laws that govern flows in electricity networks. To elucidate the electrical structure of power grids, we propose a new method for representing electrical structure as a weighted graph. This analogous representation is based on electrical distance rather than topological connections. A comparison of these two representations of the test power grids reveals dramatic differences between the electrical and topological structure of electrical power systems.

Explicit routing algorithms for Internet traffic engineering

Abstract: This paper considers explicit routing algorithms for Internet traffic engineering. Explicit routing is seen to be a much more capable solution for improving network utilization than the current destination-based routing and the multi-protocol label switching (MPLS) standard has made explicit routes implementable. ISP can now have fine granularity control over the traffic distribution across their backbones by carefully overlaying explicit routes over the physical network. The basic traffic engineering problem is how to set up explicit routes to meet bandwidth demands between the edge nodes of the network and at the same time to optimize the network performance. We model the traffic engineering problem as an optimization problem with the objective of minimizing congestion and maximizing potential for traffic growth. We present two mathematical formulations, one linear programming for the case of allowing demand bifurcation and one integer programming for the case of disallowing demand bifurcation. While the bifurcation case can be solved to optimality, we show that the non-bifurcation case is NP-hard. Four heuristic schemes are proposed for the non-bifurcation case, with the most sophisticated one being based on re-routing of split demands in the optimal solution of the bifurcation case. The performance of these heuristic schemes are tested in a large backbone topology. Our results show that shortest-path and minimum hop algorithms, although widely used in current routing protocols, perform poorly, white the re-routing approach performs best.

Traffic Aware Scheduling Algorithm for reliable low-power multi-hop IEEE 802.15.4e networks

Abstract: The Time Synchronized Channel Hopping (TSCH) protocol is part of the newly defined IEEE 802.15.4e standard and represents the latest generation of highly reliable low-power MAC protocols. With implementation details left open, we conceive here a novel Traffic Aware Scheduling Algorithm (TASA) by extending the theoretically well-established graph theory methods of matching and coloring by means of an innovative approach based on network topology and traffic load. TASA is able to support emerging industrial applications requiring low latency at low duty cycle and power consumption. Preliminary simulation results have also been reported to highlight the effectiveness of the proposed algorithm.

Power efficient topologies for wireless sensor networks

Abstract: Wireless sensor networks have become possible because of the on-going improvements in sensor technology and VLSI. One issue in smart sensor networks is achieving efficient operation because of the limited available power. For important classes of sensor networks, such as biomedical sensors, the locations of the sensing nodes are fixed and the placement can be pre-determined. In this paper, we consider the topology that best supports communication among these sensor nodes. We propose a power-aware routing protocol and simulate the performance, showing that our routing protocol adapts routes to the available power. This leads to a reduction in the total power used as well as more even power usage across nodes. We consider different routes and topologies, demonstrating the difference in performance and explaining the underlying causes.